They are probably recruiting locally (from amongst criminal elements or those at risk of becoming criminals) as well as from over the border.
Youth without work or those working for the smuggling networks. They could be offering a high wage then could be earned any other way. mapping this human terrain is a crucial part of identifying the whole operation.
Also why the economy needs to be ramped up in there areas ASAP, but with a clear indication that anyone that takes part in these criminal activities will not be given an amnesty down the road and will not be able to get a job in any new project.